In recent years, exercise balls have become popular among people who want a simple, low impact device to assist them with stretching and toning exercises. These balls typically are 18 to 26 inches in diameter, made of a strong and resilient material, and filled with air.
A user may engage an exercise ball in many ways, but one exercise is particularly useful. During it, the user squats with feet on the floor so that he is face up and his back is supported by the ball. He then alternately extends and bends his legs, thereby alternately arching and flattening his back by rocking back and forth on the ball.
Although exercise balls are useful and effective, they do have some inherent problems. One problem is that a ball can be difficult to control. Because it is free to roll, it is unstable and can move in unintended directions. A related problem is that it allows an unrestricted range of motion, even though safe exercising demands a restricted and predictable range of motion. And a third problem is that it takes up a good deal of space when not in use.
A variety of modifications have been offered with the intention of solving one or more of these problems. For example, one approach has involved using a cup-like base into which an exercise ball fits, thereby restricting the movement of the ball during use. Another approach involves using an exercise ball that is rotatably mounted to a frame so that the ball rotates only about a single axis.
Other non-ball devices have been proposed that accommodate rocking motions similar to those that can be performed on exercise balls. For example, one approach has involved using an arcuate lounge that rocks back and forth on a surface in response to the user's leg and foot movements. Another exercise device incorporates a frame that supports a flexible chair, which rocks as the user contracts and relaxes selected muscles. Another abdominal exerciser incorporates a frame-supported bench that rocks side to side in response to a user's movements relative to the frame. And another exercise device includes arcuate frame elements that rock on a surface in response to a user's contraction and relaxation of the abdominal muscles.
Although prior art devices are useful, none has the functionality of an exercise ball while eliminating all of its inherent problems. Accordingly, there is clearly a need for an improved exercise device. Ideally, such a device would accomplish the following: a) simulate part of a ball's shape; b) be stable during use; c) allow a limited and predictable range of motion; and d) fold compactly and quickly for easy storage. The present invention provides such a device.